Berthierine and Chamosite Hydrothermal: Genetic Guides in the Pena˜ Colorada Magnetite-Bearing Ore Deposit, Mexico

Earth Planets Space, 58, 1389–1400, 2006

Berthierine and chamosite hydrothermal: genetic guides in the Pena˜ Colorada magnetite-bearing ore deposit, Mexico

M. L. Rivas-Sanchez1, L. M. Alva-Valdivia1, J. Arenas-Alatorre2, J. Urrutia-Fucugauchi1, M. Ruiz-Sandoval3, and M. A. Ramos-Molina3

1 Laboratorio de Paleomagnetismo y Geof´ısica Nuclear, Instituto de Geof´ısica, Universidad Nacional Autonoma´ de Mexico,´ Mexico´ (D. F.) 04510 Mexico´ 2 Laboratorio Central de Microscop´ıa, Instituto de F´ısica, Universidad Nacional Autonoma´ de Mexico,´ Mexico´ (D. F.) 04510 Mexico´ 3 Direccion´ General y Direccion´ de Tecnolog´ıa, Consorcio Minero Benito Juarez,´ Pena˜ Colorada, S. A. de C. V., Av. del Trabajo No. 1000, Manzanillo, Colima, Mexico´

(Received December 14, 2005; Revised June 1, 2006; Accepted June 6, 2006; Online published November 8, 2006)

We report the first finding of berthierine and chamosite in Mexico. They occur in the iron-ore deposit of Pena˜ Colorada, Colima. Their genetic characteristics show two different mineralization events associated mainly to the magnetite ore. Berthierine is an Fe-rich and Mg-low 1:1 layer phyllosilicate of hydrothermal sedimentary origin. Its structure is 7 A,˚ dhkl [1 0 0] basal spacing and low degree structural ordering. The phyllosilicate has been identified by a lack of 14 A˚ basal reflection on X-ray diffraction (XRD) patterns. These data were supported by High Resolution Transmision Electron Microscopy (HRTEM) images that show thick packets of berthierine in well defined parallel plates. From the analysis of Fast Fourier Transform (FFT), we found around [1 0 0] reflections of berhierine 7.12 A˚ and corresponding angles of hexagonal crystalline structure. Berthierine has a microcrystalline structure, dark green color, and high refraction index (1.64 to 1.65). Birefringence is low, near 0.007 to null and it is associated to nanoparticles (<15 nm) and microparticles of magnetite (<25 μm), fine grain siderite, and organic matter. Its texture is intergranular–interstratified with colloform banding. The chamosite Mg-rich is of hydrothermal epigenetic origin affected by low-degree metamorphism. It is an Fe-rich 2:1 layer silicate, with basal space of 14 A,˚ dhkl [0 0 1]. The chamosite occurs as lamellar in sizes ranging from 50 to 150 μm. It has intense green color and refraction index from 1.64 to 1.65. The birefringence is near 0.008, with biaxial (-) orientation and a 2V small. It is associated mainly to sericite, epidote, clay, feldspar, and magnetite. Chamosite is emplaced in open spaces filling and linings. Mossbauer¨ spectra of berthierine and chamosite are similar. They show the typical spectra of paramagnetic substances, with two well defined unfoldings corresponding to the oxidation state of Fe+2 and Fe+3. Chemical composition of both minerals was obtained by an electron probe X-ray micro-analyzer (EPMA). The radio Fe+Mg+Mn vs Si and Al show similar chemical compositions and different XRD patterns in the crystalline structure provoked by the environmental conditions of emplacement. A hydrothermal environment was predominant, occurring before, during, and after the magnetite mineralization. The identification of magnetite nanoparticles supports the hypothesis of a marine environment, specifically exhalative sedimentary (SEDEX) for the berthierine. Key words: Berthierine, chamosite, magnetite nanoparticles, iron-ore, SEDEX, Pena˜ Colorada, Mexico.

1. Introduction thrust zone (Yoshida, 1998), in metamorphic rock in the Berthierine and chamosite are relatively scarce minerals Sierra Albarrana pegmatite body (Del Mar Abad-Ortega in nature, approximately just around 15 localities around and Nieto, 1995), in the coal-swamp deposits in Paleo- the world are known associated to iron deposits. Some are gene and Upper Triassic coal, Japan (Iijima and Matsumoto, SEDEX in origin (Damyanov and Vassileva, 2001; Xu and 1982). Veblen, 1996; Kimberley, 1989; Curtis and Spears, 1968 This is the ﬁrst report of berthierine and chamosite in the Wiewiora et al., 1998), other sulﬁde massive volcanogenic magnetite-bearing ore deposit of Pena˜ Colorada, Mexico.´ (Slack et al., 1992), metamorphic origin (Wybrecht et al., It is located to the north of the Sierra Madre del Sur, in 1985), and associated to bauxite and laterite (White et al., the northwestern part of the Colima State (Fig. 1). It is 1985; Toth and Fritz, 1997). These minerals also occur in the major iron-ore deposit of Mexico. It has 173 million Northampton ironstone (Hirt and Gehring, 1991), in pale- tons of ore reserves of high-grade Fe magnetic. We made osol near Waterval Onder, South Africa (Retallack, 1986), mineralogical, physicochemical, and textural studies of the in the oolitic ironstone beds, Hazara, Lesser Himalayan high-degree-of-purity berthierine and chamosite obtained through a metallurgical process, together with other repre- Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sci- ences (SGEPSS); The Seismological Society of Japan; The Volcanological Society sentative minerals associated to the main ore (magnetite). of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sci- Berthierine and chamosite are considered good indicators ences; TERRAPUB. of the geological processes and conditions under which this

1389 1390 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

Fig. 1. Localization of the study area. deposit was formed. Thus, they represent an important key stratified orebody; (2) breccia stockwork-type and veins of in the knowledge of the environmental characteristics that magnetite with chamosite. 500 samples from both areas contribute to the formation of important iron-ore deposits were obtained using a systematic sampling and divided in in the world (Damyanov and Vassileva, 2001; Slack et al., two groups: (1) Base samples, with the representative char- 1992; Bhattacharyya, 1983). The results obtained support acter of the deposit (mineralogical associations and textu- the hypothesis of a SEDEX origin for this deposit. ral relations); and (2) Samples from metallurgical processes SEDEX deposits are formed from the hydrothermal fluid to obtain products such as magnetic and nonmagnetic con- discharge on the Earth crust surface in a marine environ- centrates. The last ones were separated by density to erase ment. The basins of extensional type provoke the tectonic the background produced by the associated minerals, which activity that accompanied the fluid ascent along the active result in a high proportion of high purity chamosite and faults and the discharge through the hot springs, producing berthierine. This purity was controlled by direct optical chemical precipitation (exhalites) deposited on the marine microscopy, high-quality images were obtained by optical floor. The constant repetition of hydrothermal fluids dis- microscopy, XRD and HRTEM. charge and the exhalite formation provoke sedimentation Base samples and metallurgical products (concentrates) processes, compaction and diagenesis during the evolution were examined under transmitted and reflected light mi- of the sedimentary basin (Pirajno, 1992). These processes croscopy using a Leitz SM-LUX-POL polarized micro- are important components in the formation of exhalative scope. More that 200 thin and polished sections were stud- sedimentary deposits. ied. The optical properties were studied in each separated For the mineralogical characterization we applied several crystal of chamosite and berthierine using oil immersion. methodologies to analyze berthierine and chamosite miner- They present refractive index ranging from 1.56 to 1.70. als associated to magnetite and their textural relations (size For identification purposes, shape and orientation were con- and shape). Main objectives include: (1) studies of min- trolled. eralogical features, mineral association and texture rela- The berthierine and chamosite concentrates were ana- tion that were completed using reflected-transmitted light lyzed by XRD Simens D-500 using Cu-Kα (λ = 1.5418 microscopy, XRD, EPMA and Mossbauer¨ spectroscopy; A)˚ in conditions of 40 kV and 30 mA. Representative (2) identification of magnetite nanoparticles investigated base samples and magnetic and non-magnetic concentrates through HRTEM. of each type of mineral (berthierine and chamosite) were This study shows a complex mineralogy divided into selected for detailed analysis. The XRD patterns from two paragenetic types: (1) chamosite of hydrothermal epi- selected samples were prepared by the standard methods genetic origin associated mainly to massive/disseminated heated at 550◦C for 1 hour. The purpose was to pro- magnetite-sericite-clay mineral quartz and epidote; and (2) voke alteration of the crystalline structure of berthierine and berthierine of hydrothermal origin, due to hydrothermal- chamosite to corroborate the kaolin-type and chlorite-type ism and diagenetic processes in a SEDEX environment. structure for berthierine and chamosite, respectively, fol- Berthierine is associated to siderite, organic matter and lowing the Bailey (1988) method. The kaolin-type structure micro-nanoparticles of botryoidal magnetite. is characteristic of diagenetic chlorite formed in a marine sedimentary exhalative environment. Polytype identifica- 2. Material and Methodology tion was according to Bailey (1988) and Carroll (1970). In the Pena˜ Colorada iron-ore deposit, there are two Representative areas of berthierine and chamosite were well differentiated zones because of their mineralogical selected in the base samples in function of their mode of oc- and textural association of magnetite with berthierine and currence and mineral association to be studied by EPMA in chamosite: (1) magnetite-berthierine intergranular in a order to get their chemical composition. We used a JEOL, M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL 1391

Table 1. Mineralogical and textural characteristics of berthierine and chamosite. Mineral Berthierine Chamosite Structure Stratiform body Mineralized breccia stockwork type Origin Hydrothermal-sedimentary Hydrothermal-epigenetic Laminar shape Microcrystalline Amorphous Colloform Recrystallized Laminar with veins

Color Dark green Brown-green Dark green Bright greenish Olive green Olive green size < 5 μm 0 < 100 μm < 35 μm 20-200 μm 15-300 n (1) 1.64 - 1.65 1,65 1.64 - 1.65 1.64 - 1.65 1.64-1.65 1.64 - 1.65 Birrefringence 0,007 Zero 0,007 Near to 0.008 0,008 0,008 Mineral association Botryoidal magnetite, Botryoidal magnetite, Magnetite, siderite, botryoidal- Magnetite massive veins, Berthierine and Siderite, calcite, calcite, quartz, siderite, botryoidal magnetite, Magnetite, feldespars, calcite, quartz, Magnetite. organic matter, organic matter, sulphides. calcite, sulphides. calcite, quartz, sericita, epidote, sulphides. quartz. sulphides. Mode of occurrence Intergranular matrix. Intergranular lining- Colloform banding recrystallized- Open space filling and Magnetite,quartz in botryoidal magnetite berthierine replaced the host rocks. and berthierine Intergranular matrix. Intergranular- colloform banding with magnetite in veins. Figure 2a 2b 2, c, d. 2 e, f 8 a, b, c. 8 d

(1) R efraction index.

Table 2. Representative multielemental analyses (wt%) and structural formulae of berthierine.

Ocurrencia Intergranular Colloform banding Recrystallized Polytype Ib Ib IIb Origin Hidrothermal-sedimentary Hidrothermal-Sed High grade-diagenetic Sample No.A - 3 A - 309 A - 318A - 46 A-MM-5 A - 31D SiO2 30,47 30,52 29,03 29,31 23,72 28,39 30,30 27,45 24,25 TiO2 0,02 0,04 0,00 0,01 0,00 0,32 0,00 0,00 0,00 Al2O3 14,85 15,27 14,38 14,20 17,62 14,60 18,25 18,11 26,29 FeO 45,70 46,61 47,16 48,06 44,55 46,07 32,66 40,03 35,90 MnO 0,46 0,51 0,48 0,52 0,00 0,44 0,00 0,00 3,01 MgO 4,99 5,01 6,02 5,98 7,66 4,69 6,36 7,82 5,11 CaO 0,47 0,28 0,18 0,15 0,00 0,29 0,00 0,70 0,01 Na2O 0,05 0,02 0,02 n. d. 0,00 0,02 0,00 0,00 0,03 K2O 0,07 0,10 0,01 0,05 0,00 0,17 0,00 0,00 0,01 Cl n. d. n. d. n. d. 0,10 0,00 n. d. 0,00 0,00 0,28 Cr2O3 0,04 n. d. 0,03 n. d. 0,00 0,01 0,00 0,33 0,05 NiO n. d. n. d. n. d. n. d. 0,00 0,01 0,00 2,90 0,00 97,12 98,35 97,31 98,37 0,00 94,99 87,57 97,34 94,94 Si 6,345 6,291 6,113 6,120 5,981 5,913 5,737 5,652 4,978 IVAl 1,655 1,709 1,887 1,880 2,02 2,087 2,263 2,348 3,022 VIAl 2,006 2,013 1,692 1,629 2,236 1,514 1,837 2,062 3,381 Ti 0,002 0,007 n. d. 0,002 0,000 0,505 0 0,000 0,000 Cr 0,006 n. d. 0,006 n. d. 0,000 0,001 0 0,054 0,008 Fe3+ 0,187 0,164 n. d. n. d. 0,121 0,223 0 0,000 0,256 Fe2+ 7,772 7,872 8,388 8,479 7,233 7,802 9,219 6,989 5,907 Mn 0,081 0,088 0,085 0,091 0,000 0,078 0 0,000 0,524 Mg 1,550 1,540 1,889 1,860 2,254 1,456 1,186 2,400 1,563 Ni n. d. n. d. n. d. 0,001 0,000 0,001 0 0,480 0,000 Ca 0,104 0,061 0,041 0,034 0,000 0,065 0 0,154 0,002 Na 0,040 0,016 0,016 0,000 0,000 0,012 0 0,000 0,021 K 0,038 0,050 0,006 0,024 0,000 0,091 0 0,000 0,006 Cl n. d. n. d. n. d. 0,071 0,000 n. d. 0 0,000 0,191 OH* 16,000 16,000 16,000 15,929 16,000 16,000 16 16,000 15,809 35,786 35,812 36,123 36,120 35,845 35,748 36,264 36,139 35,669

AlTotal 3,661 3,722 3,580 3,509 4,255 3,601 4,1 4,410 6,403

Fe Total 7,959 8,036 8,388 8,479 7,354 7,88 9,219 6,989 6,163 Fe/(Fe+Mg) 0,83 0,84 0,82 0,82 0,77 0,85 0,74 0,744 0,798 Fe+Mg+Mn 8,04 8,12 8,47 10,43 9,608 9,55 10,405 9,389 7,766 Oct. 11,786 11,811 12,123 12,12 11,844 11,748 12,242 12,139 11,668 Al/Si 0,6 0,6 0,6 0,6 0,7 0,6 0,714 0,8 1,3 Mg/Fe 0,19 0,19 0,22 0,22 0,31 0,18 0,13 0,34 0,25 M:Or(1) Or Or Or Or Or Or Or M Or M

(1) M:Or signifies ratio of M (monoclinic) to Or (orthorhombic) form.

JXA 8900-R microscope, with 20 Kv acceleration voltage and allows analysis of nanometer-order specimen areas. and 20 sec acquisition time. The electron-microprobe analyses used the standards SPI#02753-AB. 3. Ocurrence of Berthierine and Chamosite Mossbauer¨ spectroscopy analyses of berthierine and Chamosite and berthierine are minerals of limited oc- chamosite were completed in order to obtain details of their currence in nature, and important components in the iron- chemical characteristics. The Mossbauer¨ spectra were ob- ore deposit of Pena˜ Colorada. By virtue of their compo- tained at room temperature with a constant acceleration sition, texture, and mineralogical associations, chamosite transducer and 512 multichannel analyzer: the velocity cal- and berthierine could act out as a record of the chemical ibration was performed with a laser interferometer referred and physical conditions existing during the iron-ore gen- to metallic iron, -source of 57Co/Rh. esis. Thus, we can understand the origin, environment The High Resolution Transmission Electron Microscope of deposition, hydrothermal alteration, and metamorphism (HRTEM) studies were completed using a JEOL 2010 FEG that occurred in the Pena˜ Colorada deposit. Berthierine is FASTEM, with a spherical aberration coefﬁcient of Cs =0.5 clearly differentiated from chamosite because its dark green nm and a point resolution ≈ 1.94 A˚ at an acceleration volt- to brown color, microcrystalline to amourphous shape, and age of 200 kV. This offers a resolution better than 0.2 nm very low (<0.007) to null birefringence. The main miner- 1392 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

Fig. 2. Optical microscope microphotographs of the berthierine: (a) Microcrystalline berthierine (B) of A-3 sample forming an intergranular matrix with magnetite (M); (b) Amorphous berthierine showing microcrystalline areas forming intergranular texture with magnetite, sample A-309. Amorphous berthierine clearly shows null birefringency (isotropy). Quartz veins (Q) and calcite (Ca) cut the berthierine; (c) Colloform bands berthierine of sample A-46 in contact with magnetite and calcite; (d) Colloform berthierine along the borders of magnetite, associated to siderite (Se) and calcite (sample A-46); (e) Botryoidal magnetite in intergranular berthierine matrix partly recrystallized (sample A-MM-5); (f) Magnetite-berthierine of intergranular texture (sample A-38). alogical and textural characteristics of the berthierine and 3.1.1 Optical microscopy Berthierine has very fine chamosite are reported in Table 1. microcrystalline to amorphous grain size. It is present in 3.1 Berthierine three varieties depending of its texture and mineralogical The berthierine belongs to the chlorite group. It is a associations (Fig. 2): (1) berthierine-magnetite intergran- phyllosilicate chemically and closely related to chorites, but ular; (2) berthierine in colloform banding and open space structurally related to serpentine. It has a layered structure, filling; (3) berthierine recrystallized. Berthierine is distin- each layer having a tetrahedral (Si, Al)2O5 component, and guished of chamosite because of its intense dark green and linked to a tri-octahedral (brucite-type) component (Deer, brown color along the magnetite contact. It markedly shows 1993). This latter component is similar to ferriferrous clay pleochroism from greenish yellow to grass green, the in- mineral (Bhattacharyya, 1983). The general composition terference tints are masked by the mineral color. It has a 2+ 3+ of berthierine is Y6Z4O10(OH)8,(Y=Fe , Mg, Fe , Al; high refraction index from 1.64 to 1.65 and birefringence Z=Si, Al, Fe+3) (Bhattacharyya, 1983). Berthierine has ranging from 0.007 to zero. Berthierine is mainly associ- Fe-Al, 1:1- type layer silicate with basal spacing of 7 A˚ ated to magnetite and in minor proportion to sulfides (pyrite (Damyanov and Vassileva, 2001). and chalcopyrite), siderite, calcite, quartz and organic mat- M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL 1393 ter. Opaque minerals as magnetite and sulfur were fully studied and corroborated by optical microscopy using reflected light, XRD and SEM with multielemental analyses (EPMA). 3.1.2 X-ray difraction (XRD) We analyzed pure berthierine samples coming from intergranular, colloform banding, open space filling, and recrystallized berthierine. Figure 3 shows this three typical XRD patterns of berthierine. The spectra of the diffraction pattern (and structure) are similar to the disordered kaolinite with a lower degree of structural ordering. It does not show the reflection d=14.4 A.˚ We carried out new tests to prove the identification of berthierine. It consists in altering their structure following the Carroll (1970) procedure. Samples were calcined at 550◦C over one hour, after that the residues were analyzed by XRD. In the acquired spectra, the reflections dis- appeared showing amorphous spectrums (Fig. 3). Carroll (1970) indicates that kaolin-type chlorite gives a diffraction pattern and a heating pattern similar to kaolinite. That is, the kaolin-type structure collapses by heating at ∼550◦C and the diffraction pattern appears amorphous. The variation of chemical composition in chlorite pro- duce structures called polytypes (Bailey and Brown, 1962; Bailey, 1988, 1991). They report structures in the form of layers similar to mica, which has structural arrangements in brucite-type layers (tri-octahedral component in the net- work). They recognized that 80% of the chlorites are the Fig. 3. XRD patterns of berthierine (B) in distinct textural modes from samples heated at 550◦C. (a) Intergranular berthierine of the Ib (β=90◦) IIb polytype in which the structure is a monoclinic unit group. It shows the characteristic spectrum of samples with low degree cell. The chlorite residual is the Ib polytype based on an of structural ordering. (b) Berthierine in colloform banding and open ◦ orthohexagonal (or orthorhombic) unit cell (Carroll, 1970). space filling of the Ib (β=90 ) group, and (c) Berthierine recrystallized Berthierine belongs to this one. to chamosite (Ch) for high-degree diagenetic or low-degree metamorphic of the IIb polytype. C: calcite, Q: quartz. Berthierine has a higher content of FeO and a crystal structure similar to kaolin (orthorhombic). The biggest reflection, equivalent to 100% is dhkl=7 A˚ [001] as occuring in kaolin. Polytypes are in the function of the composition The compositional variation in the intergranular magnetite- of sheets and not of the sequence of accommodation in the berthierine is greater than the berthierine present in the mineral. Berthierine shows Ib polytype in base to its com- high-degree diagenetic zone. This latter is considerably + position, radicals R 3 replacing Al and Si, predominating more homogenous and structurally well balanced. Content an octahedral unit cell. of Si replaced by Al keep a 1:2 proportion. 3.1.3 Mineral chemistry Results of the representa- Two triangular diagrams are utilized: (1) Fe+Mg+Mn tive microprobe analyzes in wt.% and structural formulae - Si - Al and (2) Mg - Fe - Al. Both diagrams show the are presented in Table 2. A Berthierine formulae unit was composition of berthierine. They indicate the trend of atom + + calculated on the basis of 28 oxygens and with Fe2 /Fe3 numbers per formulae unit functioning in a distinct environ- and OH calculated assuming full site occupancy. It is no- ment and depositional conditions. table that the major content of FeO ranges from 32 to 48%. 3.1.4 High Resolution Transmission Electron Mi- SiO2 is between 28 to 30%, decreasing to 24% in berthier- croscope (HRTEM) The crystalline structure of berthierine samples that are affected by high-degree diagenetic. ine is formed by packages ordered in parallel form. Some Content of MgO is low (4 a 7%). CaO, Na2O, K2O, Ca2O3 layers are deformed and in other fields the structure is sur- < and MnO is also low 0.7%. TiO2 was undetected in most rounded by an amorphous phase which supports the XRD samples, and is <0.04% when present. results. In this amorphous phase are located the botryoidal The content of H2O is total and does not make any differ- micro- and nanoparticles of magnetite (Fig. 4). Those parti- ence between H2O+ y H2O-. Octahedral cations are in the cles were identified by HRTEM defining the main interpla- range 0.74 to 0.85, reaching up to 3.0 in metamorphosed nar distances of magnetite with values dhkl=3.06 A˚ [220], samples. The tetrahedral Al cation is in the range from 2.56 A˚ [311] (Rivas-Sanchez et al., in prep.). x=1.6 to 2.3 atoms per formulae unit. The interplanar distance corresponds to the values: The three types of berthierine differ in their chemi- dhkl=7 A˚ [0 0 1], 3.52 [0 0 2], 4.3 [1 0 0] and 2.5 [1 1 1] cal composition (Table 2). The intergranular berthierine (Figs. 5 and 6). Diffraction patterns support the suggested has low Al content and more vacant octahedral positions interplanar distances. The angle measurements from the than colloform banding and open space filling berthierine. Fast Fourier Transform show an hexagonal type crystalline 1394 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

Fig. 6. High resolution (HRTEM) image obtained from sample A-3. Fig. 4. High resolution (HRTEM) image obtained from sample A-3. (a) Berthierine structure showing the interplanar distances corresponding Crystalline structure of berthierine arranged in packages forming paral- to values dhkl=2.5 A˚ [111] and 3.5 A˚ [002]. Inset, FFT image suggests lel layers surrounded by an amorphous phase with null to low degree of that berthierine is oriented in [111] direction. estructural ordering. (b) Amorphous phase berthierine. (c) Magnetite nanopart´ıculas distributed in the amorphous phase of berthierine.

Fig. 7. Mossbauer¨ spectroscopy apectrum showing the typical quadrupolar unfolding of two oxidation states: FeO and Fe2O3.

Fig. 5. High resolution (HRTEM) image obtained from sample A-3. general composition is (Mg, Fe, Al)6 (Al, Si)4O10 (OH)8. Crystalline structure of berthierine showing interplanar distances corre- Fe2 is the dominant composite, Al is in lower proportion, sponding to the values dhkl=7.1 A˚ [001], 3.5 A˚ [002] and 4.3 A˚ [100]. Inset, FFT images indicates that the berthierine is orientated in [001] and Mg and Si are slightly higher. direction. The formation of polytypes is due to the equilibrium of the available energy in the environment. Chlorite is formed, in stable conditions, as a result of low-degree metamor- structure (Fig. 5) that corresponds to an orthorhombic unit phism under medium to high-temperature and it is IIb poly- cell (Brindley and Youell, 1953) or to a trigonal unit cell type. (Brindley, 1951). 3.2.1 Optical microscopy Chamosite has a laminar 3.1.5 Mossbauer¨ spectroscopy The study of shape, sheets measure from 20 to 200 μm (Fig. 8). Two berthierine shows quadrupolar unfolding typical of two types of chamosite were observed, based on its texture and states of oxidation; FeO and Fe2O3 (Fig. 7). mode of occurrence: (1) open space ﬁlling chamosite; and 3.2 Chamosite (2) chamosite with veins of colloform banding of berthier- The chamosite structure is very similar to typical chlorite ine. Chamosite is associated with the host rock, gener- in which there are alternated regular layers with tetrahedral ally completely replacing feldspar hornfels through veins and tri-octahedral components. Its 2:1 layer structure is and fractures, altered rocks, and low-degree metamorphism. similar to that of mica, with a basal spacing of 14 A.˚ The It represents the beginning of the hydrothermal phase. M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL 1395

Fig. 8. Optical microscope microphotographs of the chamosite. (a) Lamellar chamosite. (b) Chamosite replacing the host rock and ﬁlling open spaces in magnetite (M). (c) Chamosite lamella partly replaced by berthierine (B) along its borders. d) Lamellar chamosite with berthierine veins and magnetite.

Chamosite is distinguished because of its olive green color with remarkable pleochroism from greenish to light green. It has a high index refraction (1.64–1.65). Its birefringence is low, near 0.008 (Fig. 8). Orientation is Biaxial (-) with a 2V small. The cleavage are length-slow, the orientation may be α ∧ c=small, β=b, γ ∧ α=small, optic plane=[0 1 0] (Heinrich, 1965). 3.2.2 X-Ray diffraction The chamosite spectra shows the reflection d=7.18 A˚ (main value of the chlorite) and the reflection d=14.4 A˚ (that confirms the presence of chlorite) (Fig. 9). Using the heating method (Brindley, 1961; Carroll, 1970), we observed that chamosite did not collapse at 550◦C, the chlorite value d=14 A˚ increased, and d=7 A˚ decreased (Fig. 9). Thus, the order of refraction intensity is different. Chamosite with a similar structure to typical chlorite does not collapse at 550◦C. However, there are changes in the intensity of the values of the main reflection, like value d=7.18 A˚ (100%), that appears to be smaller with respect to the secondary reflection d=14.2 A˚ (70%). 3.2.3 Mineral chemistry Results of representative microprobe analyses in % wt and the structural formulae are presented in Table 3. Chamosite formulae units were used on the basis of 28 oxygens and with Fe2+/Fe3+ and OH, calculated assuming full-site occupancy. Chamosite has an important amount of Fe ranging from 23 to 39%. SiO2 re- Fig. 9. XRD patterns of chamosite in distinct textural modes and min- mains decreasing between 26 and 35%. The MgO content is eralogical association from samples heated at 550◦C. (a) IIb polytype high, ranging from 11 to 20%, and Fe2O3, Na2O, K2O and lamellar chamosite shows a characteristic spectrum with a high degree of structural ordering. (b) Lamellar chamosite with berthierine veins. MnO are low <2%. TiO2 was undetected in most samples, < Berthierine replaces chamosite through fractures following a replace- and is 0.2% when present. ment front. The content of H2O is total and does not make any dif- 1396 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

4. Discussion Table 3. Representative multielemental analyses (wt%) and structural The chemical and mineralogical characterization of formulae of chamosite. chamosite and berthierine show that both minerals are Shape Laminar Replaced for berthierine Polytype IIb IIb chemically related but are structurally different. Their close Origin Hydrothermal-epigenetic Hydrothermal Sample No. N - 239 N - 3 textural relation with magnetite allows a better understand- SiO2 29,37 27,40 29,44 29,72 33,31 35,29 26,19 TiO2 0,00 0,00 0,03 0,29 0,00 0,01 0,00 ing of its origin and deposition environment. Tables 2 and Al2O3 17,95 16,20 15,68 16,53 13,81 17,23 15,67 FeO 28,66 39,39 36,72 37,40 31,78 23,38 27,20 3 show the main chemical and structural characteristics of MnO 1,15 0,00 1,63 1,32 1,93 1,11 1,20 MgO 17,44 11,19 12,42 12,17 12,48 20,48 12,76 both mineral varieties. CaO 0,44 0,00 1,49 0,25 3,15 2,66 0,39 Na2O 0,00 0,00 0,04 0,00 0,00 0,10 1,02 Chamosite is related to the beginning of a hydrother- K2O 0,00 0,00 0,18 0,05 0,00 0,00 0,01 ZnO 0,00 0,00 0,51 0,58 1,26 0,00 0,00 mal phase and occurs mainly in a mineralized breccia type Cl 0,44 0,00 0,76 0,77 0,66 0,00 0,58 Cr2O3 0,00 0,00 0,25 0,00 0,02 0,01 0,00 stockwork, in which it fills open spaces and replaces the NiO 0,00 0,00 0,85 0,00 0,00 0,01 0,72 host rock through fissures. It is associated to magnetite, 95,45 94,18 100 99,08 98,40 100,28 85,74 Si 5,753 5,719 5,762 5,872 5,839 6,348 6,385 sulphide, epidote, calcite, quartz, feldspar, clay minerals, IVAl 2,25 2,281 2,238 2,128 2,161 1,652 1,615 VIAl 1,917 1,737 1,427 1,74 2,01 2,016 2,190 and sericite. The chamosite-magnetite textural relationship Ti 0,000 0,00 0,004 0,043 0,00 0,001 0,007 is characterized by magnetite in veins cutting the host rock Cr 0,000 0,000 0,039 0,00 0,00 0,001 0,00 Fe3+ 0,000 0,000 0 0,002 0,061 0,190 0,16 replaced by chamosite and epidote, forming a mineralized Fe2+ 4,758 7,101 6,178 6,178 5,061 3,327 4,596 Mn 0,190 0,000 0,27 0,221 0,315 0,169 0,213 breccia. This association permits us to demonstrate the epi- Mg 5,091 3,48 3,624 3,59 3,59 5,49 3,980 Zn 0,000 0,00 0,074 0,09 0,18 0,00 0,000 genetic hydrothermal origin for magnetite, after deposition Ni 0,000 0,000 0,134 0,000 0,00 0,001 0,009 Ca 0,093 0 0,313 0,053 0,65 0,514 0,087 of chamosite and epidote. After the hydrothermal magnetite Na 0,003 0,000 0,031 0,000 0,000 0,068 0,83 K 0,000 0,000 0,091 0,024 0,000 0,001 0,004 deposition, follows the deposition of calcite, quartz, and Cl 0,290 0,00 0,657 0,52 0,431 0,00 0,046 OH* 15,710 16,000 15,343 15,484 15,569 16,000 15,954 sulfurs (mainly pyrite and chalcopyrite). These last min- 36,052 36,320 36,185 35,932 35,860 35,778 36,079 erals fills open spaces in magnetite. AlTotal 4,165 4,018 3,665 3,869 4,166 3,668 3,805

Fe Total 4,758 7,101 6,178 6,18 5,122 3,517 4,759 Berthierine is the most abundant chlorite, keeps a 5:1 Fe/(Fe+Mg) 0,48 0,671 0,63 0,63 0,59 0,39 0,545 Fe+Mg+Mn 10,039 10,582 10,071 9,984 9,022 9,176 7,997 proportion with chamosite, and is related to the final Oct. 12,052 12,318 12,185 11,908 11,86 11,778 12,076 Al/Si 0,7 0,7 0,6 0,7 0,8 0,58 0,6 stage of the hydrothermalism of a mineralized stratiform Mg/Fe 1,07 0,49 0,59 0,58 0,75 1,56 0,84 (1) body. Some samples show incipient recrystallization pro- M:Or MMMMM~Or Or>M Or>M voked by low-degree metamorphism or by high-grade di- (1) M:Or signifies ratio of M (monoclinic) to Or (orthorhombic) form. agenetic. It is strongly intergrowed into an intergranular shape with botryoidal magnetite of micro- nanometric size, and in colloform belt shapes that fill open spaces into the magnetite-ore. It is related to siderite, calcite, sulfide and organic matter (Fig. 11). Berthierine is a mineral formed by diagenetic processes from chemical precipitates (exhalites) of hydrothernmal origin that were deposited on the marine bottom. The close textural relationship of berthierine with botryoidal magnetite of very fine micrometric size (mean 20 μm) and nanometric size (mean 6 nm) show a common environment of formation, related to exhalative sedimentary (SEDEX) origin. Optical properties show clear differences between chamosite and berthierine. Berthierine depict because of its very fine grain size (<15 μm) becoming amorphous, and chamosite is distinguished because of its lamellar shape. Berthierine shows more intense colors (dark green and Fig. 10. Mossbauer¨ spectra showing the typical quadrupolar unfolding of brown) and strong pleochroism. Both minerals coincide in two states of oxidation: FeO and Fe2O3. refraction index, ranging from 1.64 to 1.65, with low birefringence (<0.008) that sometimes is null for berthierine. ˚ ference between H2O+yH2O-. Octahedral cations are in The XRD data show: (1) chamosite with 14 A basal the range 0.39 to 0.67%. The tetrahedral Al cation is in spacing, and (2) berthierine with 7 A˚ basal spacing. The the range from x=1.61 to 2.28 atoms per formulae unit and absence of the 14 A˚ reflection is decisive in identification with lower octahedral occupancy. It is structurally well bal- of the berthierine (Brindley, 1982). anced but much more variable chemically. XRD data of berthierine affected by low-degree meta- Two triangular diagrams were utilized: (1) Fe+Mg+Mn morphism or high-degree diagenesis (Fig. 3) shows that - Si - Al and (2) Mg - Fe - Al. Both diagrams show a compo- the 14 A˚ basal spacing is very weak, thus we suppose sition of chamosite that indicates the trend of atoms number that berthierine is at the initial phase of transformation per formulae unit functioning in a distinct environment and to chamosite. The XRD data and microprobe analy- depositional conditions. ses (EPMA) gave support to the knowledge of structural 3.2.4 Mossbauer¨ spectroscopy The chamosite spec- arrangement types, by mean of calculation of dominant trum shows the quadrupolar unfolding typical of two states cations (octahedral or tetrahedral) and ions number into the of oxidation: FeO and Fe2O3 (Fig. 10). structural formulae. M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL 1397

Fig. 11. Microphotographs of berthierine showing mineralogical associations and textural relations. (a) Berthierine (B) in an intergranular matriz with magnetite (black) in micrometric and nanometric scale; (b) Berthierine (B) with quartz veins (Q) and calcite (Ca) ﬁlling open spaces in the berthierine and quartz; (c) Colloform band of berthierine ﬁlling open spaces between magnetite (black) and calcite (Ca); (d) Pyrite (Pi) surrounded progressively by siderite (Se) and granular quartz (Q).

In base of the structural formulae: Y6Z4O10(OH)8, (Y=Fe2+, Mg, Fe3+, Al; Z=Si, Al, Fe+3), we calculated the corresponding parameters for the octahedral and tetrahedral components, and the ion number into the structural formulae of the chamosite and berthierine. The intergranular and colloform banding of berthierine present a Ib polytype structural arrangement with a particu- lar chemical composition, where R+3 radicals substitute Al and Si forming an orthorhombic (Bailey and Brown, 1962; Brindley, 1951, 1982) or trigonal unit cell (Brindley, 1951, 1982). A Fourier transform image from the HRTEM study shows an hexagonal component [001] [110], supporting the trigonal unit cell. In some areas, the berthierine recrystal- lizes and the unit cell parameters change from Ib to IIb polytype, showing a monoclinic unit cell (M). Then the d=14 Fig. 12. Fe/(Fe+Mg) vs IVAl diagram of berthierine and chamosite. Oc- A˚ values appear and monoclinic is greater than orthorhom- currence of intergranular berthierine (open diamonds) and berthierine in ≥ colloform banding and open space ﬁlling (open triangles), predominate bic (M Or) (Table 3). Diagenetic chlorite are Ib polytype, polytype Ib, and IIb for recrystallized berthierine (open circles). Poly- and during the diagenetic process they change to IIb due to type IIb dominate in vein of chamosite (solid diamonds), however, in recrystallization (Carroll, 1970). The IIb polytype is dom- chamosite replaced by berthierine through veins (solid triangles) domi- inant in chamosite with the characteristic monoclinic unit nate Ib polytype. cell in which a major amount of Al - Si radicals dominate, in the function of the R+3=Fe/(Fe+Mg) (Bailey, 1962, 1988) (Fig. 12). Brindley and Youell (1953) demonstrate that both The octahedral totals are lower than the theoretical orthorhombic and monoclinic polytypes co-exist in variable (12.0) value for tri-octahedral component of chamosite and proportions. berthierine (11.94 ions per unit formulae). The chamosite Chamosite replaced by berthierine in fractures suffers has a mean value of 12.02 ions per formulae unit. The ion changes in its unit cell predominating Al tetrahedral over vacant number into the octahedral component ranges from Si. We observed that an increase in AlIV vs a decrease of 0.092 to 0.222 for chamosite, and from 0.156 to 0.332 for ionic radio of Si, together with substitution of octahedral Fe berthierine. The tetrahedral total for chamosite ranges from by Mg, decrease notably the FeO. 1.165 to 2.281 IVAl ions and from 1.65 to 2.26 IVAl ions 1398 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

Fig. 13. VIAI vs IVAl diagrams for berthierine and chamosite in their distinct occurrences.

Fig. 15. (a) Al - Mg - Fe triangle diagram (Velde, 1985; Damyanov and Vassileva, 2001). The berthierine field (open diamonds, open triangles, and open circles) is wider than the proposed by these authors and is in the marine zone. Recrystallized berthierine (open circles) is also in the ore zone. (b) Al - Mg - Fe triangle diagram (Velde, 1985; Damyanov and Vassileva, 2001). The chamosite field (solid diamonds) of vein open space filling and of replacement is in the pre-ore zone. Chamosite associated to berthierine (solid triangles) is out of the pre-ore zone.

ponents possibly due to substitution of Fe ions by Mg. In berthierine, the predominance is of three main textural pre- sentations. In this case, intergranular berthierine contains a minor number of IVAl components in respect to berthierine affected by metamorphism or diagenesis in which occur a notable increase of components of IVAl with a decrease of Fig. 14. Mg/Fe vs Al/Si diagram (Damyanov and Vassileva, 2001). Berthierine data from distinct occurrences (open diamonds, triangles, Si and Fe ions by Mg substitution. and circles) suggests a marine origin. Figure 14 shows that the marine environment emplacement of the intergranular berthierine (higher content of Mg/Fe) is different to that of metamorphosed berthierine for berthierine per formulae unit. These data show that (higher Al/Si). Chemical composition variation of berthier- chamosite has a unit cell more homogeneous and struc- ine and chamosite are presented in Figs. 15 and 16. Based turally well balanced as opposed to berthierine which has in the microprobe analyses (EPMA), we calculated the a more unstable unit cell and major number of octahedral cationic relationship by formulae unit for the construction vacants. of the diagrams Fe+Mg+Mn-Si-AlandMg-Fe-Al. The relationship between octahedral Al (VIAI) and tetra- The diagram of Fig. 15 shows the close relationship of hedral Al (IVAl) is shown in Fig. 13 for different textural berthierine and chamosite with the ore (magnetite) before, types of chamosite and berthierine. The chamosite that oc- during ,and after deposition of hydrothermal magnetite. cupy open spaces in the host rocks (veins) contain a major The berthierine samples with a high cation tetrahedral IVAl amount of IVAl in respect to chamosite associated to collo- value (recrystallized berthierine) are located in the high- form berthierine, which depicts the increasing of VIAI com- degree diagenetic and low-degree metamorphic zone. M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL 1399

Fig. 17. EPMA images. (a) Berthierine (B) forming an intergranular matrix with magnetite (M), sample M-3. (b) Lamellar chamosite (Ch) replacing the host rock in the mineralized breccia type stockwork (massive magnetite veins (M), sample A-31D.

Fig. 16. a) R2+–Al–Si triangle diagram (Velde, 1985; Damyanov and Vassileva, 2001). The berthierine compositions (open diamonds and tri- ical texture of deposition in a sedimentary exhalative envi- angles) are in the ore zone in contrast with the recrystallized berthierine ronment (Fig. 17). The amorphous phase of berthierine is (open circles) that is in the high-grade diagenetic/metamorphic chlo- attributed to an intense ionic change, where Fe replaces Mg rite zone. b) R2+–Al–Si triangle diagram (Velde, 1985; Damyanov and Vassileva, 2001). The chamosite compositions (solid diamonds and tri- in the dominant octahedral positions of the berthierine for- angles) are in the ore zone. mulae unit. The end of the hydrothermal phase is indicated by the presence of berthierine ﬁlling open spaces and forming colloform bands contiguous to magnetite grains. Berthierine is also associated to siderite and organic mat- Most of chamosite samples belong to the pre-ore zone ter. Precipitation of siderite occur when there is a low con- in the triangular diagram (Fig. 15), suggesting that they are centration of iron sulfur (pyrite), high accumulation of car- emplaced at the beginning of the hydrothermal phase, be- bonates and Fe, high Fe2+/Ca radio, low Eh and pH close fore deposition of magnetite and vein sulphides. Berthier- to 7. ine is in the marine zone, corresponding to a sedimentary The emplacement of berthierine-magnetite exhalative hy- exhalative hydrothermal process (SEDEX). Marine chim- drothermal took place after chamosite deposition and it is neys produced the hydrothermal Fe rich brines, in a marine related to the more important stratiform structure into the clay ﬂoor of relatively shallow depth, provoking the simul- Pena˜ Colorada deposit. taneous precipitation of intergranular berthierine and mag- McDowell and Elders (1980) use authigenic phyllosili- netite. The berthierine with colloform bands was emplaced cates in sedimentary deposits to determine the thermal gra- afterwards. dient, considering the microprobe chlorite analyses. They The sedimentary hydrothermal phase is associated to suc- found that low total octahedral (−11.0 corresponds to tem- cessive phases of diagenetic precipitation, which occur dur- perature of 150◦C) relates to relatively shallow depth and ing and after precipitation of magnetite (Fig. 16). This closed unit cell (with a theoretical value of 12) at a temper- hydrothermal-diagenetic process supplied the formation of ature of 360◦C. microcrystalline and amorphous berthierine, strongly asso- Chamosite has a low total octahedric mean=12.02 per ciated to botryoidal magnetite of micro- and nanometric formulae unit. Therefore, correspond to a crystallization sizes. Both minerals form the intergranular texture. The temperature close to 360◦C. Berthierine has total octahedric botryoidal texture of magnetite in berthierine shows the typ- mean=11.94 corresponding to a crystallization temperature 1400 M. L. RIVAS-SANCHEZ et al.: BERTHIERINE AND CHAMOSITE HYDROTHERMAL

◦ close to 150 C. mineralogy, 19, 179–181, 1991. Two main genetic episodes occur during the berthierine Bailey, S. W. and B. E. Brown, Chorite polytypism: I. Regular and semi- and chamosite formation in the Pena˜ Colorada Mine: (1) random one-layer structures, Americal Mineral., 47, 819–850, 1962. Bhattacharyya, D. P., Origin of berthierine in ironstones, Clays and Clay The berthierine of hydrothermal origin precipitates by dia- Minerals, 31(3), 173–182, 1983. genetic processes at the sea bottom; (2) The chamosite of Brindley, G. W., Chemical compositions of berthierine—a review, Clays hydrothermal origin was emplaced in open spaces into the and clay Minerals, 30(2), 151–155, 1982. Brindley, G. W., The crystal structures of some chamosite minerals, Min- host rock (there is replacement evidence, Fig. 16 and 17). eral. Mag., 29, 502–525, 1951. A high concentration of Al has been observed in recent Brindley, G. W., Kaolin, serpentine, and Kindred minerals, in The X-ray geothermal areas associated to marine basins, which sug- Identification and Crystal Structures of Clay Minerals, edited by G. gests the importance of the Al phyllosilicates, particularly Brown, Mineralogical Society London, pp. 51–131, 1961. Brindley, G. W. and R. F. Youell, Ferrous chamosite and ferric chamosite, berthierine of SEDEX deposits (Damyanov and Vassileva, Mineralog. Mag., 30, 220, 57–70, 1953. 2001). This relationship allows the use of berthierine and Carroll, D., Clay Minerals: A Guide to their X-ray Identification, The chamosite as geologic environment indicators. Geological Society of America, Special Paper, 126, 1970. Curtis, C. D. and D. A. Spears, The formation of sedimentary Iron Miner- als, Econ. Geol., 67, 257–270, 1968. 5. Conclusions Damyanov, Z. and M. Vassileva, Authigenic phyllosilicates in the middle By virtue of its composition, texture, and mineralogical Triassic Kremikovtsi sedimentary exhalative siderite iron formation, associations of chamosite and berthierine, two mineraliza- Western Balkan, Bulgaria, Clays and Clay Minerals, 49, 6, 559–585, tion stages and environment of deposition, closely related 2001. Deer, W. A., R. A. Howie, and J. Zussman, Rock-Forming Minerals. Vol. 5 to the main magnetite ore are recognized: (1) Chamosite Non-Silicates, John Wiley and Sons Inc., pp. 62–124, 1993. epigenetic hydrothermal; and (2) Berthierine hydrothermal Del Mar Abad-Ortega, M. and F. Nieto, Extension and closure of the sedimentary exhalative (SEDEX). compositional gap between Mn and Mg rich chorites toward Fe-rich The first hydrothermal process in the Pena˜ Colorada de- compositions, European J. Mineral., 7(2), 363–367, 1995. Hayes, J. B., Polytypism of chorite in sedimentary rocks, Clays and Clay posit took place at the end of the Cretaceous epoch, and is Minerals, 18, 285–306, 1970. characterized by chamosite replacing the host rock (feldspar Heinrich, E. W., Microscopic Identification of Minerals, McGraw-Hill hornfels) through fractures and filling open spaces in the Book Company, 1965. same host rock. This host rock produced a mineralized Hirt, A. M. and A. U. Gehring, Thermal alteration of the magnetic mineralogy in ferruginous rocks, J. Geophys. Res., 96(B6), 9947–9953, 1991. breccia type stockwork, with massive magnetite veins cut- Iijima, A. and R. Matsumoto, Berthierine and chamosite in coal measures ting the host rock in several directions. Chamosite is asso- of Japan, Clay and clay Minerals, 30(4), 264–274, 1982. ciated to magnetite, sericite, clay minerals, quartz, epidote Kimberley, M., Exhalative origins of iron formations, Ore Geol. Rev., 5, and sulfides. 13145, 1989. McDowell, S. D. and W. A. Elders, Authigenic layer silicate minerals The berthierine precipitation during and after magnetite in borehole Elmore I, Salton Sea geothermal field, California, USA, deposition indicate the end of the hydrothermal phase, pos- Contrib. Mineral. Petrol., 74, 293–310, 1980. sibly at the beginning of Tertiary. Berthierine was formed Pirajno, F., Hydrothermal mineral deposits, in Principles and Fundamental Concepts for the Exploration Geologist, SpringerVerlag Berlin Heidel- by hydrothermal and diagenetic processes in a marine sed- berg, 1992. imentary exhalative environment (SEDEX). This environ- Retallack, G., Reappraisal of a 2200 Ma-old paleosol near Waterval Onder, ment was favorable for the very fine grain (microcrystalline South Africa, Precambrian Res., 32(2-3), 195–232, 1986. to amorphous) berthierine deposition. Berthierine occurs Slack, J. F., J. Wel-The, D. R. Peacor, and P. M. Okita, Hydrothermal and metamorphic berthierine from the Kidd Creek volcanogenic massive mainly in two textural shapes: (1) intergranular; and (2) fill- sulfide deposit, Timmins, Ontario, Can. Mineralogist, 30, 1127–1142, ing open spaces in the host rock forming colloform bands. 1992. Berthierine is associated to siderite, organic matter, botry- Toth, T. A. and S. J. Fritz, An Fe-berthierine from a Cretaceous laterite: oidal magnetite, and magnetite nanoparticles. The SEDEX Part I. Charaterization, Clays and Clay Minerals, 45(4), 564–579, 1997. Velde, B., Clay minerals: A physicochemical explanation of their occur- body is related to the most important stratiform structure rence, Developments in Sedimentology 40, Elsevier, Amsterdam, 1985. located in the Pena˜ Colorada iron-ore deposit. White, S. H., J. M. Huggett, and H. F. Shaw, Electron-optical studies The micro-and nanoparticles of magnetite are homoge- of phyllosilicate intergrowths in sedimentary and metamorphic rocks, neously distributed in the amorphous area of the berthierine. Mineral. Magazine, 49, 413–423, 1985. Wiewiora, A., A. Wilamowski, L. Bozena, M. Kuzniarski, and D. Grabska, They are associated with sedimentary exhalative origin. Chamosite from oolitic ironstones: The necessity of a combined XRD- EDX approach, Can. Mineralogist, 36, 1547–1557, 1998. Acknowledgments. We thank to the Consorcio Minero Benito Wybrecht, E, J. Duplay, A. Pique,´ and F. Weber, Mineralogical and chem- Juarez,´ Pena˜ Colorada for supplying the mine products. We also ical evolution of whit micas and chlorites, from diagenesis to low-grade appreciate the kind help of Ernesto Aguilera Torres (Laborato- metamorphism; data from various size fractions of greywackes (Middle rio Experimental Mexico´ de la CFM), Margarita Reyes and Car- Cambrian, Morocco), Mineral. Magazine, 49, 401–411, 1985. los Linares (Laboratorio de Petrolog´ıa del Instituto de Geof´ısica, Xu, H. and D. R. Veblen, Interstratification and other reaction microstruc- UNAM) and Luis Rendon´ (Laboratorio Central de Microscop´ıa tures in the chlorite-berthierine series, Contrib. Mineral Petrol., 124, del Instituto de F´ısica). Finally, we thank the financial support of 291–301, 1996. DGAPA-UNAM research Project IN-108605. Yoshida, K., Formation of plications in the Miocene bivalve Mytilus (Pli- catomytilus) ksakurai as a consequence of architectural constraint, Pa- leontol. Res., 2(4), 224–238, 1998. References Bailey, S. W., X-Ray diffraction identification of the polytypes of mica, serpentine and chlorite, Clays and Clay Minerals, 36(3), 193–213, 1988. M. L. Rivas-Sanchez, L. M. Alva-Valdivia (e-mail: lalva@geofisica. Bailey, S. W., Structures and composition of other trioctahedral 1:1 phyl- unam.mx), J. Arenas-Alatorre, J. Urrutia-Fucugauchi, M. Ruiz-Sandoval, losilicates, Hydrous Phyllosilicates (exclusive of micas), Reviews in and M. A. Ramos-Molina